1. Field of the Invention
The present invention relates to a power control unit, or in particular to a power control unit for a data processing system capable of switching the system performance by changing the operating frequency (hereinafter referred to as the clock frequency) of a processing circuit.
2. Description of the Related Art
In recent years, an extension of the use of a high-performance CPU (central processing unit) has remarkably improved the processing capability of data processing systems such as computers which, in turn, has increased the power consumption. On the other hand, a portable terminal making up a data processing system has been reduced in size and weight while the liquid crystal display panel making up a display unit has increased in size, which is another cause of increased power consumption in the data processing system.
Due to the decreased size and weight of the portable terminal, the capacity of the battery incorporated in the portable terminal and hence the electric energy capable of being supplied are limited. In the case where it is desired to increase the clock frequency of the processing circuit or the brightness of the display unit, the power consumption may exceed the battery capacity. Some means to cope with this problem is desired.
In a conventional data processing system in which the clock frequency of a processing circuit such as a CPU or a processor can be changed, the system performance of the data processing system is changed in response to a user instruction or some change of the system status such as the insertion or removal of an AC adaptor. The system performance can be changed by changing the clock frequency of the processing circuit built into the data processing system.
Specifically, as disclosed in Unexamined Japanese Patent Publication (Kokai) No. 10-26896 and the like, one well-known methods of reducing the power consumption of the computer system consists of reducing the clock frequency of the processing circuit. According to this method, the user is permitted to select the clock frequency of the processing circuit, so that the user sets the clock frequency of the processing circuit to a low level by key entry or the like operation thereby to reduce the capacity of the computer system as a whole, resulting in a reduced power consumption.
A data processing system operating on a battery, however, generally has the problem that the operable range of the system is limited by the total or residual capacity of the battery. In the case where the clock frequency of the processing circuit is changed or, especially, the clock frequency is changed to a large value, the power consumption of the system increases sometimes to such an extent that operation on the battery is difficult. A power consumption exceeding the output capacity of the battery is a case in point.
The power consumption of the data processing system may be limited also by the thermal design. The thermal capacity tolerable for the data processing system may be exceeded, for example, in the case where the status is changed to increase the clock frequency of the processing circuit while the subsystems other than the processing circuit are operating in the data processing system.
In order to avoid this problem, the system is designed with a sufficient thermal capacity or with a battery of a sufficient capacity at the sacrifice of an increased size, weight and cost of the data processing system.
Accordingly, a first object of the invention is to provide a power control unit for a data processing system or, in particular, a power control unit for a data processing system driven by a battery, in which an increased power consumption of the whole data processing system is suppressed by reducing the power consumption in a display unit with the increase in the clock frequency of the processing circuit.
A second object of the invention is to provide a power control unit for a data processing system or, in particular, a power control unit for a data processing system driven by a battery, in which the increase in power consumption of the data-processing system as a whole is suppressed by reducing the clock frequency of the processing circuit in the case where the brightness of the display unit is increased.
A third object of the invention is to provide a power control unit for a data processing system or, in particular, a power control unit for a data processing system driven by a battery, in which the increase in power consumption of the data processing system as a whole is suppressed by reducing the clock frequency of the processing circuit temporarily at the time of spinup of the drive motor for a disk-shaped recording medium.
The features of the invention for achieving the aforementioned objects of the invention are described as first to third aspects thereof below.
According to the first aspect of the invention, there is provided a power control unit for a data processing system having a system performance capable of being switched by changing the clock frequency of a processing circuit, comprising a circuit for reducing the power consumption by reducing the brightness of a display unit connected to the data processing system in the case where the clock frequency of the processing circuit is increased, and a circuit for increasing the power consumption by increasing the brightness of a display unit connected to the data processing system in the case where the clock frequency of the processing circuit is decreased.
According to the second aspect of the invention, there is provided a power control unit for a data processing system having a system performance capable of being switched by changing the clock frequency of a processing circuit, comprising a circuit for reducing the clock frequency of the processing circuit in the case where the brightness of the display unit connected to the data processing system is increased and a circuit for increasing the clock frequency of the processing circuit in the case where the brightness of the display unit connected to the data processing system is decreased.
According to the third aspect of the invention, there is provided a power control unit for a data processing system having a system performance capable of being switched by changing the clock frequency of a processing circuit, comprising a circuit for reducing the clock frequency of the processing circuit at the time of spinup of the drive motor for a disk-shaped recording medium built in the data processing system and a circuit for restoring the clock frequency of the processing circuit to the original state at the end of the spinup operation of the drive motor.
In the first to third aspects described above, the data processing system can be a notebook-sized personal computer, and the display unit can be a liquid crystal display panel.
In the first aspect, the power consumption of the display unit is reduced by the decrease in the brightness thereof in the case where the clock frequency of the processing circuit of the data processing system is increased, while the power consumption of the display unit is increased by increasing the brightness thereof in the case where the clock frequency of the processing circuit is decreased, and therefore the power consumption of the data processing system as a whole is not increased beyond a specified value.
In the second aspect, the clock frequency of the processing circuit is decreased in the case where the brightness of the display unit of the data processing system is increased, while the clock frequency of the processing circuit is increased with the decrease in the brightness of the display unit, and therefore the power consumption of the data processing system as a whole is not increased beyond a specified value.
In the third aspect, the clock frequency of the processing circuit is decreased at the time of spinup of the drive motor for the disk-shaped recording medium while the clock frequency of the processing circuit is restored to the original state at the end of the spinup operation, and therefore the power consumption of the data processing system as a whole is not increased beyond a specified value.
The present invention according to the first to third aspects thereof can be realized with a notebook-sized personal computer having a liquid crystal panel as a display unit.